Optical fiber communication systems are now widely deployed. Recently, relatively new communication services, such as the Internet, high-speed data links, video services, wireless services and CATV, have resulted in a dramatic increase in the need for higher information data rates. The aggregate data throughput rate of a communication system is typically increased by increasing at least one of the bandwidth of the individual data channels and the number of data channels.
State-of-the art optical fiber communication systems are being built to transmit data over long distances with higher data rates and/or with a larger number of data channels. In addition, state-of-the art optical fiber communication systems often include features, such as gain management, wavelength multiplexing, tunability, and switching. Furthermore, state-of-the art optical communications systems are agile, flexible, and reconfigurable. Many features of these state-of-the art networks are automated.
These state-of-the art optical communications systems typically require monitoring throughout the system. In these state-of-the-art systems, it is typically necessary to measure the optical power and the optical signal-to-noise ratio (OSNR) of WDM signals. It is also desirable to measure the power of the optical noise at the same wavelength as the signal, which is sometimes called the “in-band” optical signal-to-noise ratio.